Egypt tense on third anniversary of revolution
Rival political groups in Egypt are to mark the third anniversary of the 2011 uprising which ended in the overthrow of President Hosni Mubarak.
Both supporters of the military-backed government and the Muslim Brotherhood are set to take to the streets.
The anniversary comes as tensions were heightened by a series of bombs in Cairo and clashes across the country which left at least 18 people dead.
The government has said extra security measures are in place for Saturday.
"We have a plan to secure all of this for the anniversary of the 25 January revolution," Egyptian Interior Minister Muhammad Ibrahim said.
He urged Egyptians not to be afraid to go to events marking the anniversary. However, earlier this week he warned supporters of the Brotherhood that any attempt to "disrupt" festivities will be dealt with "firmly".
The Brotherhood has held regular protests since the military, led by Gen Abdel Fattah al-Sisi, deposed Islamist President Mohammed Morsi last July.
The Anti-Coup Alliance, led by Mr Morsi's Muslim Brotherhood, called in a statement for 18 days of protests beginning on Saturday, mirroring the 18 days of protests that led to Mubarak stepping down in 2011.
The Brotherhood has been declared a "terrorist organisation" and accused by the interim government of being behind a string of violent attacks in recent months, which the Brotherhood denies.
Morsi, Egypt's first ever democratically elected president, was removed after mass protests. Many now expect Gen Sisi to run for president, putting a military strongman back in charge in Egypt, as was the case for the six decades leading up to 2011.
ANGER AT BROTHERHOOD
On Friday six people were killed and some 100 others wounded in a series of blasts across Cairo, with the biggest blast outside the city's police headquarters.
That explosion killed four people and wounded at least 76, laving a huge crater in the street.
Correspondents say the security directorate is a very significant target and should have been one of the best protected buildings in the city.
Hours later, there were three more blasts elsewhere in the city, killing two people and injuring several more.
Local media report that an al-Qaeda-inspired militant group, Ansar Beit al-Maqdis (Champions of Jerusalem), has said it carried out the attack on the police headquarters.
The group previously claimed responsibility for a car bomb attack on a security building in the northern city of Mansoura in December that killed 16 people and injured more than 100 others.
An angry group gathered outside the bombed police headquarters after the blast, accusing the Brotherhood of being behind Friday's attacks. Some shouted "Death to the Muslim Brotherhood".
The Muslim Brotherhood condemned what it called the "cowardly bombings".
Meanwhile, 12 people were reported killed in clashes between security forces and Muslim Brotherhood supporters in Cairo and several other provinces on Friday.
The interior ministry said it had arrested 111 people, saying they were "Brotherhood elements" who were "trying to provoke riots".
One of the demands of the uprising three years ago was more freedom for Egyptians after three decades of authoritarian rule under Mubarak.
However Saturday's commemorations take place at a time when human rights organisations say rights and liberties in the country are being eroded.